Skeletal Muscle Adaptive Responses to Different Types of Short-Term Exercise Training and Detraining in Middle-Age Men

Marcus J. Callahan; Evelyn B. Parr; Tim Snijders; Miguel S. Conceição; Bridget E. Radford; Ryan G. Timmins; Brooke L. Devlin; John A. Hawley; Donny M. Camera


Med Sci Sports Exerc. 2021;53(10):2023-2036. 

In This Article

Abstract and Introduction


Introduction: Whether short-term, single-mode exercise training can improve physical fitness before a period of reduced physical activity (e.g., postsurgery recovery) is not well characterized in clinical populations or middle-age adults. We investigated skeletal muscle adaptive responses after endurance exercise training (ENT), high-intensity interval training (HIIT), or resistance exercise training (RET), and a subsequent period of detraining, in sedentary, middle-age men.

Methods: Thirty-five sedentary men (39 ± 3 yr) were randomized to parallel groups and undertook 6 wk of either ENT (n = 12), HIIT (n = 12), or RET (n = 11) followed by 2.5 wk of detraining. Skeletal muscle fiber characteristics, body composition, muscle thickness, muscle strength, aerobic capacity, resting energy expenditure, and glucose homeostasis were assessed at baseline, and after exercise training and detraining.

Results: Lean mass increased after RET and HIIT (+3.2% ± 1.6% and +1.6% ± 2.1%, P < 0.05). Muscle strength (sum of leg press, leg extension, and bench press one-repetition maximums) increased after all training interventions (RET, +25% ± 5%; HIIT, +10% ± 5%; ENT, +7% ± 7%; P < 0.05). Aerobic capacity increased only after HIIT and ENT (+14% ± 7% and +11% ± 11%, P < 0.05). Type I and II muscle fiber size increased for all groups after training (main effect of time, P < 0.05). After a period of detraining, the gains in lean mass and maximal muscle strength were maintained in the RET and HIIT groups, but maximal aerobic capacity declined below posttraining levels in HIIT and ENT (P < 0.05).

Conclusions: Six weeks of HIIT induced widespread adaptations before detraining in middle-age men. Exercise training–induced increases in aerobic capacity declined during 2.5 wk of detraining, but gains in lean mass and muscle strength were maintained.


Exercise training enhances physical fitness (muscle strength and aerobic capacity) resulting in marked improvements in metabolic health and functional capacity.[1] As such, intense exercise training before a period of forced or planned inactivity (i.e., injury or postsurgery) is a common practice as a strategy to augment preoperative physical fitness and postoperative recovery.[2–4] Preoperative exercise training prescription is based on general exercise training guidelines emphasizing combined endurance and resistance exercise training.[5] However, whether implementation of both exercise modalities reflects optimal programming for all preoperative settings is questionable.[6,7]

Although combined exercise training can induce robust changes in muscle strength and aerobic capacity over extended time periods (≥12 wk),[8] many individuals have to undergo surgery at short notice and do not have time to undertake such exercise training regimens.[4] As such, it is important to determine the short-term, mode-specific effects of exercise training on multiple components of physical fitness. Defining short-term muscle adaption responses to different exercise training modalities in healthy middle-age adults is important to provide evidence-based guidelines for short-term preoperative exercise training programming.

Six weeks of aerobic-based exercise training increases aerobic capacity.[9–12] However, the short-term effects of such training interventions on muscle strength are less clear. Another important aspect of physical fitness is skeletal muscle mass, which is necessary for mobility and whole-body glycemic control.[13,14] Individuals with low muscle mass before surgery are at increased risk of adverse postoperative outcomes such as major surgery–related complications, prolonged hospital length of stay, morbidity, and mortality.[15–18] However, comparisons between short-term exercise training modalities on markers of whole-body and regional muscle mass in middle-age adults are lacking.

Another knowledge gap regarding muscle adaptation responses are the effects of short-term exercise training cessation (i.e., detraining) subsequent to divergent exercise training modalities. Detraining is the partial or complete loss of exercise training–induced adaptations due to a reduction or cessation in exercise frequency, intensity, or duration.[19] In the early postoperative period (i.e., the first few weeks after surgery), exercise training may not be feasible because of pain, nausea, or physical restrictions.[20] As little as 2 wk of reduced physical activity can induce catabolic events in skeletal muscle, resulting in decreased muscle mass[21,22] and impaired glycemic control.[23] Whether short-term exercise training adaptations are maintained after a short detraining period in middle-age adults is unknown. Ultimately, clarification of short-term single-mode exercise training and detraining responses in healthy middle-age adults will help to inform preoperative exercise training programming, particularly for populations tasked with time constraints before surgery.

In the current study, we tested the hypothesis that 6 wk of endurance, resistance, or high-intensity interval exercise training would induce divergent anabolic and metabolic skeletal muscle adaptive responses in middle-age men. Among the anabolic responses, we assessed vastus lateralis muscle fiber cross-sectional area (CSA) after exercise training and detraining. Here, we hypothesized that high-intensity interval training (HIIT), because of its closer resemblance in contractile intensity/activity with resistance exercise training, would induce a greater increase in muscle fiber CSA compared with endurance exercise training, although this increase would be less in magnitude compared with resistance exercise training.